1. Field of the Invention
The invention relates to a design of adjusting the position of the light tube of a scanner, and more particularly to a design which may adjust the relative distance between the light tube and the line to be scanned on the document to be scanned.
2. Description of the Related Art
An image capture device, such as a scanner, mainly uses light to be projected on a document, and the light after reflected or after penetrating may enter an optical reading device to proceed optical analysis. The light tube mounted on a common scanner has constant lightness and height, and the light tube of the scanner will be better if it has a greater lightness. When the lightness of the tube and the time for shifting out the charges from the CCD (charge coupled device) are properly selected for performing the low resolution scanning or black and white scanning, some problems may occur in the high resolution scanning or color scanning. Specifically, in the high resolution scanning or color scanning, due to the low capacity of the RAM (random access memory) in the scanner and the long period of time for shifting out the charges, the photo sensor in the scanner may be exposed to the light for a long period of time. Therefore, the CCD may be easily saturated in the high resolution scanning or color scanning.
For improving the above-mentioned problem of having a constant lightness, a manner of controlling the voltage or current of the light tube may be used, so that the light tube has different values of lightness according to the using conditions. However, the common scanner has a constant DC (direct current) voltage source, so that the pulse width has to be adjusted before adjusting the voltage. Thus, the ripple is easily caused, which produces noises. For eliminating the noises, complicated electronic members or circuit designs are needed to achieve the purpose. In addition, the noises cause instability of lightness of the light tube, which produces a blinking condition, thereby affecting the scanning result. The light tube is always subjected to the effect of changed voltage or current, thereby easily wearing the light tube and decreasing the lifetime of the light tube.